#!
$sentence = "one little,  two little, three little, Indian boys";
$word="little";

print "original sentence:$sentence\n";
$start = 0;
while( ($start=index($sentence,$word,$start)) != -1 )
{
	print "find little at:$start\n";
	substr ($sentence,$start,length($word)) = "big";
	$start++;
}
print "now sentence:$sentence";